What role do you think the Steam workshop plays in this?

Obviously the people playing the AAA franchises don't care, but when you see the sheer quantity of workshop content for some games (Cities:Skylines and Space Engineers come to mind for me, no doubt there's other examples in genres I'm less familiar with), you see how much the modding community has contributed to the commercial success of these games. I'm wondering how this factors in to steam as a whole.